Dorsal Pattern Polymorphism and Adaptation in Gambelia wislizenii (Reptilia, Lacertilia, Iguanidae)

Five pattern classes (A, B, C, C1, D) of Gambelia wislizenii are recognized and described, including their ontogenetic development and sexual dimorphism. Each pattern morph characterizes or predominates in populations of a given physiographic region. Popula- tions occurring in the northern desert basins (e.g. Lahontan and Bonneville) are polymorphic, with up to 30% of a local sample belonging to pattern classes other than that typical for the region. Polymorphism is low or nonexistent in Gambelia samples from Baja California, the Sonoran and Chihuahuan deserts. Historical and genetic events are postulated to explain the difference in variability between northern and southern populations. The Mojave desert populations are the most polymorphic, possibly due to genic influx from four surrounding northern basin and southern desert populations. The various pattern morphs of Gambelia appear to be cryptic in their respective habitats. Distinct whitish crossbands in pattern class A disrupt body form, an effect best suited to shrub-grass associations. The reticulate pattern of class D lizards conceals the animal in relatively dense,Artemisia-Atriplex shrub associations of northern deserts. The punctate pattern of the class B morph and the dorsal white dots exhibited by class C and C1 lizards are considered alternative modes of concealment in relatively exposed, sandy habitats.